ANAESTHESIA, AWARENESS AND NAP5

G.Panesar

AWARENESS

Probably the most feared complication of anaesthesia from patients

Associated with psychological trauma, PTSD and lack of trust in the medical profession

Risk of lifelong sequale

Risk of medico legal complications for the anaesthetist

AWARENESS : TYPES

Implicit awareness

Patients are unable to recall events surrounding surgery

May alter behaviour and performance after the episode

Explicit awareness

Patients can remember events surrounding surgery

Memories may be recalled spontaneously or retrieved by

questioning

Most distressing when associated with pain

INCIDENCE

NAP5 : Largest audit project to date regarding awareness

Key figures:

Incidence of AAGA Certain/probable or Possible : 1:19,600

Incidence of AAGA when NMB used : 1:8200

Incidence of AAGA when no NMB used : 1:35,900

“Most pessimistic incidence” <1 : 6000

INCIDENCE : SPECIAL GROUPS

Incidence of AAGA reports after sedation : 1: 15,500

Incidence of AAGA in cardiothoracic anaesthesia 1: 8600

Incidence of AAGA with Caesarean section : 1 : 670

Multifactorial reasons for increased incidence within these groups

RISK FACTORS FOR AWARENESS

The risk of awareness is a direct function of the depth of anaesthesia

This can be altered for 4 main reasons:

1. Inadequate dose selection

2. Problems with anaesthesia side effects

3. Lack of monitoring / detection of signs of awareness

4. Inadequate dose delivery

INADEQUATE DOSE SELECTION

Most commonly due to poor technique, e.g :

Late commencement or omission of agent

Inappropriate fixed dosing (RSI)

Dose requirement for volatile agent varies with age (+/-25%)

Dose requirement for TIVA has a (theoretically) greater variability

INADEQUATE DOSE SELECTIONResistance

Pyrexia

Hyperthyroidism

Obesity

Anxiety

Tobacco smoking

Regular, heavy alcohol use

Recreational drug use

Chronic use of sedatives

Previous and repeated exposure to anaesthetic agents

Sensitivity

i.e. Reduction in MAC

Hypocapnia,

Pregnancy

Hypothyroidism,

Hypothermia,

Hypotension,

Increased atmospheric pressure

Increasing Age

PROBLEMS WITH ANAESTHETIC SIDE EFFECTS

Reduction in depth of anaesthesia to offset:

Myocardial depression

Vasodilation

Most commonly seen in emergency & trauma surgery or emergency LSCS

LACK OF DETECTION OF SIGNS OF AWARENESS

Signs consistent with sympathetic nervous system activation:

(In the paralysed patient)

Tachycardia

Hypertension

Sweating

Lacrimation

Pupillary dilation

(in the non paralysed patient)

Movement

Grimacing

Tachypnoea

MASKING OF CLINICAL SIGNS

Sign of awareness Factors masking the sign

TachycardiaHeart block, β-blockers, hypothyroidism, autonomic

neuropathy (e.g. diabetes, renal failure)

Hypertension

Heart block, β-blockers, hypothyroidism,

vasodilators, epidural analgesia, blood loss,

autonomic neuropathy

SweatingAnti-muscarinic drugs (e.g. atropine,

glycopyrrolate)

Tear production Anti-muscarinic drugs, eye tape/ointment

Movement/grimacingNeuromuscular blocking agents, sheets covering

the patient

Tachypnoea Neuromuscular blocking agents

Pupillary dilatation and reactivity to lightAnti-muscarinic drugs, opioids, ocular pathology,

eye tape/ointment

RECOGNISING AWARENESS

Generated through sympathetic activation

Sweating

Tachycardia

Hypertension

Tear formation

Pupil dilatation and pupil reactivity to light

By the use of depth of anaesthesia monitoring

BIS

Narcotrend

aaEPx

BRICE QUESTIONNAIRE

(1) What was the last thing you remembered happening before you went to sleep?

(2) What is the first thing you remember happening on waking?

(3) Did you dream or have any other experiences whilst you were asleep?

(4) What was the worst thing about your operation?

(5) What was the next worst?

CLASSIFYING AWARENESS

FOLLOWUP

Process is open and patient led

Initial assessment at 24 hours

Follow-up review at 2 weeks:

Time to allow reflection

Patient has time to interpret events and draw conclusions

Impact of awareness may manifest

Persistent psychological impact needs input from a psychologist or psychiatrist

PTSD-type reactions should be treated with either trauma-focussed Cognitive Behavioural Therapy or Eye-Movement Desensitisation and Reprocessing

AAGA

Flashbacks

Nighmares

Anxiety

Depression

NAP 5 KEY POINT SUMMARIES

Patient characteristics

Children under-represented : why?

Young/middle aged adults over represented

Increased risk in females (?obs)

Increased risk in the obese

Majority of cases ASA 1&2

Operative characteristics

Increased risk in obstetrics (x10)

Increased risk in cardiothoracics (x2.5)

Two specialities appear under represented / carry lower risk:

Plastics

T&O spinal surgery

The largest cohort of cases is by far within the “general” category of surgery

NAP 5 KEY POINT SUMMARIES

Phase of anaesthesia

Induction and emergence both “at risk” times for AAGA

Maintenance only accounts for 34% of AAGA cases

Induction is riskier than emergence

Lack of opiate use, RSI, difficult airway management and obesity all make AAGA more likely

Lack of bodyweight dosing or “dosing by ampoule” worryingly common

Anaesthetic techniques

Use of NMB massively increases risk : 93% of reports

Lack of use of a nerve stimulator increases risk

“The combination of using NMB, not monitoring its effect, and not reversing it

together seemed to incur a risk for AAGA”

Thiopentone overrepresented massively*

Anaesthetic technique

All non propofol induction agents are over represented

No riskier volatiles

TIVA over-represented

N2O no overall difference

BIS (bizarrely) over represented

? Proportion of patients with inherent risk ?5 fold chance of repeat AAGA

In around 5% of cases there is some kind of family history

NAP 5 KEY POINT SUMMARIES

ENDING THOUGHTS

Massive audit project

Essential knowledge for both CRQ and Viva

Actually quite interesting

Probably the thing you should learn how not to do!

Management of AAGA is a key role within any department

NAP 5 laid a universal best practice framework